IQ modulation systems and methods that use separate phase and amplitude signal paths and perform modulation within a phase locked loop

ABSTRACT

A digital signal processor generates in-phase, quadrature-phase and amplitude signals from a baseband signal. A modulator modulates the in-phase and quadrature-phase signals to produce a modulated signal. A phase locked loop is responsive to the modulated signal. The phase locked loop includes a controlled oscillator having a controlled oscillator input. An amplifier includes a signal input, amplitude control input and an output. The signal input is responsive to the controlled oscillator output and the amplitude control input is responsive to the amplitude signal. The phase locked loop that is responsive to the modulated signal includes a controlled oscillator output and a feedback loop between the controlled oscillator input and the controlled oscillator output. The feedback loop includes a mixer that is responsive to a local oscillator. The modulator may be placed in the phase locked loop. In particular, the modulator may be placed in the feedback loop between the controlled oscillator output and the mixer, between the local oscillator and the mixer, or between the mixer and the controlled oscillator input.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation-in-Part (CIP) of application Ser. No.09/703,037, filed Oct. 31, 2000, now U.S. Pat. No. 6,975,686 entitled IQModulation Systems and Methods That Use Separate Phase and AmplitudeSignal Paths, assigned to the assignee of the present invention, thedisclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to modulation systems and methods, and moreparticularly to IQ modulation systems and methods.

BACKGROUND OF THE INVENTION

Modulation systems and methods are widely used in transmitters tomodulate information including voice and/or data onto a carrier. Thecarrier may be a final carrier or an intermediate carrier. The carrierfrequency can be in UHF, VHF, RF, microwave or any other frequency band.Modulators also are referred to as “mixers” or “multipliers”. Forexample, in a wireless communications terminal such as a mobileradiotelephone, a modulator can be used for the radiotelephonetransmitter.

FIG. 1 illustrates a conventional IQ modulator. As shown in FIG. 1, anIQ modulator 110, also referred to as a “quadraphase modulator” or a“quadrature modulator”, includes a quadrature splitter 120, also knownas a 90° phase shifter, and a pair of multipliers 116 a, 116 b coupledto the quadrature splitter. A controlled oscillator 115, such as aVoltage Controlled Oscillator (VCO), is coupled to the quadraturesplitter 120 to produce 90° phased shifted oscillator signals. In-phase(I) data 111 a and quadrature-phase (Q) data 111 b are coupled to arespective multiplier or mixer 116 a, 116 b. Digital input data isconverted to analog data by I Digital-to-Analog Converter (DAC) 114 aand Q DAC 114 b, respectively. The outputs of the respective DACs 114 aand 114 b are applied to the respective low pass filters 112 a and 112 bto provide the respective I and Q data inputs 111 a and 111 b. Themodulator 110 modulates the input data on a carrier by summing theoutputs of the multipliers 116 a, 116 b at a summing node 118. Themodulated carrier 113 is amplified by a power amplifier 122 andtransmitted via an antenna 124.

In modern wireless communications, wireless communications terminalssuch as mobile radiotelephones continue to decrease in size, cost and/orpower consumption. In order to satisfy these objectives, it generally isdesirable to provide IQ modulation systems and methods that can providehigh power modulation while reducing the amount of battery power that isconsumed. Unfortunately, the power amplifier 122 of an IQ modulator mayconsume excessive power due to efficiency limitations therein. Morespecifically, it is known to provide a linear class-A or class-AB poweramplifier 122 that may have efficiencies as low as 30 percent or less.Thus, large amounts of battery power may be wasted as heat. Moreover,the noise figure of a conventional IQ modulator may be excessive so thathigh cost Surface Acoustic Wave (SAW) filters may need to be used.

FIG. 2 illustrates other conventional modulation systems. As shown inFIG. 2, I-data and Q-data is modulated on an Intermediate Frequency (IF)signal supplied by a controlled oscillator such as a voltage controlledoscillator 202 by applying the I-data and Q-data and the output of theIF voltage controlled oscillator 202 to an IQ modulator 204. The outputof the modulator is then bandpass filtered by an IF bandpass filter 206.A local oscillator 212 and an up-conversion mixer 214 are used toup-convert the output of the bandpass filter 206 to a desired radiofrequency. The output of the up-conversion mixer 214 is bandpassfiltered by a radio frequency bandpass filter 216 to reduce noise andspurious levels. The filtered signal is then amplified using a variablegain amplifier 222 to provide the appropriate signal level to a poweramplifier 226 which delivers the signal to an antenna 232 via a duplexfilter 234. Additional RF bandpass filtering 224 may be used between thevariable gain amplifier 222 and the power amplifier 226.

FIG. 3 is a block diagram of other conventional modulation systemswherein like elements to FIG. 2 are labeled with like numbers. Theapproach shown in FIG. 3 is similar to that of FIG. 2 except the IFsignal is up-converted to the RF band first and then modulated in the IQmodulator 204.

Unfortunately, in either of the conventional approaches of FIGS. 2 or 3,the IQ modulator 204, up-conversion mixer 214 and/or the variable gainamplifier 222 may generate significant amounts of additive noise andspurious levels which may need to be filtered before the signal reachesthe power amplifier 226. Systems of FIGS. 2 and 3 also may suffer fromhigh current consumption and may need to use an excessive number offilters to meet the desired output spurious level and desired noiselevel.

It also is known to separately modulate the amplitude and phase of aninput signal using an “rTheta” technique. In the rTheta technique, thephase is modulated at the oscillator, and the amplitude is modulated atthe power amplifier stage. Unfortunately, the rTheta technique mayrequire the oscillator phase locked loop to support the phase modulationbandwidth. With wide bandwidth radiotelephone signals such as TDMA andCDMA signals, it may be increasingly difficult to provide the requisitebandwidth in the oscillator phase locked loop.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide modulation systems andmethods having separate phase and amplitude signal paths. In particular,according to embodiments of the present invention, a digital signalprocessor generates in-phase, quadrature-phase and amplitude signalsfrom a baseband signal. A modulator modulates the in-phase andquadrature-phase signals to produce a modulated signal. A phase lockedloop is responsive to the modulated signal. The phase locked loopincludes a controlled oscillator having a controlled oscillator input.An amplifier includes a signal input, an amplitude or gain control inputand an output. The signal input is responsive to the controlledoscillator output and the amplitude control input is responsive to theamplitude signal.

In other embodiments according to the present invention, the in-phaseand quadrature-phase signals are normalized in-phase andquadrature-phase signals. In these embodiments, the digital signalprocessor generates the normalized in-phase signal as a respective sineor cosine of an angle theta and generates the normalizedquadrature-phase signal as a respective cosine or sine of the angletheta, where theta is an angle whose tangent is the quadrature-phasesignal divided by the in-phase signal. The amplitude signal also isnormalized and is generated as the square root of the sum of thein-phase signal squared and the quadrature-phase signal squared.

In other embodiments, the modulator is a first modulator and themodulated signal is a first modulated signal. These embodiments furthercomprise a second modulator that is responsive to the controlledoscillator output to produce a second modulated signal wherein the phaselocked loop also is responsive to the second modulated signal. Moreover,in other embodiments a power control signal also is provided and theamplitude control input is responsive to the amplitude signal and to thepower control signal.

In yet other embodiments, the phase locked loop that is responsive tothe modulated signal includes a controlled oscillator having acontrolled oscillator output and a feedback loop between the controlledoscillator input and the controlled oscillator output. The feedback loopincludes a mixer that is responsive to a local oscillator. In theseembodiments, the modulator may be placed in the phase locked loop. Insome embodiments, the modulator may be placed in the feedback loopbetween the controlled oscillator output and the mixer, between thelocal oscillator and the mixer, or between the mixer and the controlledoscillator input. Thus, modulation may take place within the phased lockloop instead of, or in addition to, taking place prior to the phasedlock loop.

Other modulation systems and methods according to embodiments of theinvention include a quadrature modulator that modulates in-phase andquadrature-phase signals to produce a modulated signal. A phase trackingsubsystem is responsive to the quadrature modulator to produce a phasesignal that is responsive to phase changes in the modulated signal andthat is independent of amplitude changes in the modulated signal. Anamplitude tracking subsystem is responsive to the modulator to producean amplitude signal that is responsive to amplitude changes in themodulated signal and that is independent of the phase changes in themodulated signal. An amplifier has a signal input, an amplitude controlinput and an output. The signal input is responsive to the phase signaland the amplitude control input is responsive to the amplitude signal.

In other embodiments, the phase tracking subsystem comprises a phaselocked loop that is responsive to the modulated signal. The phase lockedloop includes a controlled oscillator having a controlled oscillatoroutput that produces the phase signal.

In other embodiments, the amplitude tracking system includes anautomatic gain control subsystem that is responsive to the modulatedsignal to produce the amplitude signal. In some embodiments, theautomatic gain control subsystem comprises a first envelope detectorthat is responsive to the modulated signal, a second envelope detectorthat is responsive to the phase locked loop and a comparator that isresponsive to the first and second envelope detectors to produce theamplitude signal. In yet other embodiments, the automatic gain controlsubsystem comprises a first envelope detector that is responsive to themodulated signal, a second envelope detector that is responsive to theamplifier and a comparator that is responsive to the first and secondenvelope detectors to produce the amplitude signal. In still otherembodiments, the amplitude tracking system comprises an envelopedetector that is responsive to the modulated signal to produce theamplitude signal.

In still other embodiments, the phase tracking system comprises a phaselocked loop that is responsive to the modulated signal. The phased lockloop includes a controlled oscillator having a controlled oscillatorinput and a controlled oscillator output that produces the phase signal.The phase locked loop also includes a feedback loop between thecontrolled oscillator input and the controlled oscillator output. Thefeedback loop includes a mixer that is responsive to a local oscillator.The modulator is placed in the phase locked loop. In some embodiments,the modulator is placed in the feedback loop between the controlledoscillator output and the mixer, between the local oscillator and themixer, or between the mixer and the controlled oscillator input.Accordingly, the modulation may take place within the feedback loop inaddition to taking place before the phase locked loop.

In all of the above-described embodiments, an optional power amplifiermay be included that is responsive to the output of the amplifier havinga signal input, an amplitude control input and an output. Alternatively,a power amplifier itself may have the signal input, the amplitudecontrol input and the output. A transmit antenna is responsive to theamplifier or power amplifier.

Moreover, in all of the above-described embodiments, the amplifier mayinclude a variable gain amplifier and/or a power amplifier, at least oneof which includes an amplitude control input that is responsive to theamplitude signal. When both a variable gain amplifier and a poweramplifier are used, the variable gain amplifier may precede the poweramplifier or the power amplifier may precede the variable gainamplifier, regardless of which one includes the amplitude control input.Additional variable gain amplifiers and/or power amplifiers also may beincluded in the amplifier.

Finally , a user interface may be provided that generates the basebandsignal or the in-phase and quadrature-phase signals in response to userinput to provide a wireless communications terminal such as aradiotelephone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1–3 are block diagrams of conventional IQ modulators; and

FIGS. 4–22 are block diagrams of IQ modulation systems and methodsaccording to embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout. It will be understood thatwhen an element is referred to as being “between” other elements, it canbe directly between the other elements or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly between” other elements, there are no intervening elementspresent.

Embodiments of the present invention stem from a realization thatpotential shortcomings of the systems of FIGS. 2 and 3 may arise fromthe two mixing (heterodyning) operations that are performed. Inparticular, a frequency mixing occurs in the up-conversion mixer 214 andin the IQ modulator 204 which may include two double balanced mixers.The frequency mixing may inherently generate high spurious levels and/ornoise. Moreover, while some spurious levels far from the transmitcarrier can be attenuated by the filters 206, 216 and 224, other levelsmay be within the allowed transmission band of the transmitter and maynot be filtered. Moreover, the amount of filtering to reduce the outputnoise and spurious levels may exceed that which can be achieved with asingle RF filter. Thus, multiple filters may need to be placed in themodulator. This also can add cost and/or space to the system. Finally,in order to reduce distortion of the modulated signal (information plusthe carrier) and to meet transmit voice quality needs, the up-conversionmixer 214, the IQ modulator 204 and the variable gain amplifier 222 mayrun at high current levels, which can reduce the operating time andgenerate excessive heat for portable wireless communication terminals.

Embodiments of the present invention can reduce the output noise and/orspurious levels so that the need for additional filters may be reducedand preferably may be eliminated. Moreover, the current consumption ofan IQ modulator can be reduced while still meeting a desired linearity.

Referring now to FIG. 4, modulation systems and methods according toembodiments of the present invention are shown. As shown in FIG. 4,these embodiments of modulation systems and methods 400 include aquadrature (IQ) modulator 420 that modulates in-phase andquadrature-phase signals, referred to as I-data and Q-data, that may begenerated by a user interface 410 in response to user commands, toproduce a modulated signal 422. A phase tracking subsystem 430 isresponsive to the quadrature modulator 420 to produce a phase signal 432that is responsive to phase changes in the modulated signal 422 and thatis independent of amplitude changes in the modulated signal 422. Anamplitude tracking subsystem 440 also is included that is responsive tothe modulator 420 to produce an amplitude signal 442 that is responsiveto amplitude changes in the modulated signal and that is independent ofphase changes in the modulated signal 422. An amplifier 450 includes asignal input, an amplitude or gain control input and an output. Thesignal input is responsive to the phase signal 432. The amplitudecontrol input is responsive to the amplitude signal 442 and the outputis applied to a transmit antenna 470, optionally via a power amplifier460. Alternatively, the amplifier 450 may be a power amplifier.

Referring now to FIG. 5, other modulation systems and methods accordingto embodiments of the present invention are shown. As shown in FIG. 5,these modulation systems and methods 500 include an IQ modulator 420, aphase tracking subsystem 430′, an amplitude tracking subsystem 440′, anamplifier 450, a power amplifier 460 and an antenna 470. As shown, thetransmitter carrier frequency is generated using a fundamental radiofrequency controlled oscillator such as a voltage controlled oscillator532 which can have an extremely high signal-to-noise ratio, on the orderof −165 dBc/Hz at 45 MHz away. The output signal level is controlledusing an amplifier 450 such as a saturated variable gain amplifier. Theinformation signal (I-data and Q-data) is first modulated on an IFsignal using the IQ modulator 420. The IF signal is generated by aseparate fundamental controlled oscillator such as a voltage controlledoscillator 510. The modulated signal then is provided to separateamplitude and phase tracking subsystems in the form of amplitude andphase tracking loops 440′ and 430′, respectively. The modulated IFsignal 422 acts as a reference for amplitude and phase comparators inthe two corresponding tracking loops 440′ and 430′. The RF output signalfrom the amplifier 450 is mixed down to the IF frequency using a systemlocal oscillator 534. The VCO 532 is phase locked using the phase lockedloop that includes dividers 535 a, 535 b, a phase-frequency detector ora phase detector 537, a pair of low pass filters 538 a and 538 b, and alimiter 539. This phase locked loop acts as the channel synthesizer forthe transmitter. The output of the mixer 533 is low pass filtered vialow pass filter 538 b and fed to the limiter 539 along with themodulated reference IF signal 534.

In the phase tracking loop 430′, optional RF dividers 535 a and 535 bare placed in the reference and compare arms of the phase-frequencydetector 537 to divide by M and N respectively. Since practicalimplementation of phase-frequency detectors at high frequencies may bedifficult, this can allow for the lowering of the comparison frequencyand can have negligible effect on the phase comparison. It also will beunderstood that the dividers 535 a and 535 b may be set such that M=N,or M=N=1, or may be eliminated.

In the amplitude-tracking loop 440′, a pair of matched envelopedetectors 442 a and 442 b are used to compare the amplitude level of thedown-converted IF signal or other signal from the phase locked loop tothat of the modulated signal 422. Good matching between the two envelopedetectors 442 a and 442 b may be provided to reduce AM offsets in theloop. Also, an adjustable constant delay element 445 may be introducedin the amplitude tracking loop 440′ to match the total group delay forthe amplitude and phase signals. If the total delay is not matched, theoutput signal may not have the desired modulation characteristics.

Since the output power level of the transmitter is controlled by theamplifier 450 (VGA1) over a wide range, the total loop gain may changefor the amplitude and phase tracking loops. In the phase tracking loop,the limiter 539 and/or the limiting action of the phase detector 537 canmaintain constant loop gain, while in the amplitude tracking loop 440′,a separate variable gain amplifier 446 (VGA2) with the opposite gainversus control voltage slope as the amplifier 450 is used. As the gainof VGA1 450 is reduced to reduce output signal level, the gain of VGA2446 may be increased by the same amount to keep the signal level intothe matched envelope detectors 442 a, 442 b nearly constant. Otherwise,the envelope detectors 442 a, 442 b may need to have good matching overa very large (>50 dB) range of signal levels at the input. Such widedynamic range envelope detectors may be difficult to implement. Oneadditional potential advantage of embodiments of FIG. 5 is that theAM/PM distortion in VGA1 450 is compensated in the phase tracking loop430′. This can help achieve low phase and amplitude error over a widerange of output power levels.

The output signals of the phase and amplitude detectors are filteredusing low-pass filters 538 a, 444 which can have bandwidths large enoughto pass the modulation signal (baseband) but narrow enough to suppressnoise and spurious levels outside the modulation bandwidth. In effect,the low-pass filters 538 a, 538 b and 444 in the phase and amplitudetracking loops 440′ and 430′ can act as bandpass filters on the RFtransmit carrier signal with very narrow bandwidth (i.e., very high-Q).For example, for 30 kHz modulation bandwidth (common to digital wirelessphones), the low-pass filter bandwidth can be less than 1 MHz.Therefore, the low-pass filter in the loop can be equivalent to abandpass filter centered at the transmit frequency (e.g., 825 MHz)having a bandwidth of less than 1 MHz (Q>825). The noise and spuriouslevels outside the 1 MHz bandwidth around the carrier are attenuatedaccording to the attenuation characteristics of the low-pass filters inthe tracking loops. Such low-pass filters can be implemented withresistors and capacitors, and thus can eliminate the need for expensive,multiple SAW filters.

Direct amplitude modulation of power amplifiers (especially saturatedclass-D power amplifiers) may be known. Some embodiments of theinvention can provide electrical isolation between the modulation loopand the antenna. For example, embodiments of FIG. 5 can utilize thepower amplifier 460 as an isolator providing electrical isolationbetween the antenna 470 and the transmit modulator. In this case, theefficiency of the amplifier (VGA1) 450 may not be as important to theoverall power consumption. Therefore, it can be easier to implementsimultaneous AM modulation and large power control range in VGA1. Theamplifier 450 can be designed to operate in a fixed high-efficiency,linear mode without the need for dynamic bias adjustment. Alternatively,other embodiments can amplitude modulate the power amplifier itself.This can provide enhanced linearity margin and/or enhanced efficiency byutilizing a saturating power amplifier and restoring envelope amplitudethrough modulation of its supply.

FIG. 6 depicts embodiments of the present invention in a half-duplexsystem such as a TDMA-only IS-136 terminal or an EDGE terminal. In thiscase, the signal-to-noise ratio of the transmitter can be high enough sothat the duplexer filter 480 of FIG. 5 can be replaced by atransmit-receive (T/R) switch 580 in the transmit path. Also in FIG. 6,the power amplifier 460 itself is amplitude modulated.

It also will be understood by those having skill in the art that inFIGS. 5 and 6, the input to the mixer 533 may be taken between the VCO532 and the amplifier 450 rather than between the output of theamplifier 450 and the power amplifier 460 as illustrated.

FIG. 7 is a block diagram of other modulation systems and methodsaccording to embodiments of the invention. In these embodiments, theamplitude tracking subsystem 440″ is implemented as a direct modulationor an open loop. This may be accomplished, for example, if an amplifier450 having a linear voltage control characteristic is used. Such acircuit is feasible with integrated circuit design techniques. Forembodiments of FIG. 7, the divide ratio of the phase locked loop is oneso that M and N are set to 1 or no dividers 535 a, 535 b are used. TheIF amplifier 746 after the down-converting mixer 533 can be either avariable gain amplifier or an AGC amplifier. This amplifier 746 may beused in order to reduce the input operating range of the limiter 539.The AM/PM distortion of the limiter 539 thereby can be reduced. In FIG.7 the amplitude tracking subsystem 440″ includes an envelope detector742 such as a diode and an adjustable delay 445.

FIG. 8 depicts embodiments that can be used in a half-duplex system suchas a TDMA-only IS-136 terminal or an EDGE terminal. In FIG. 8, thesignal-to-noise ratio of the transmitter can be high enough so that theduplexer filter 480 can be replaced by a transmit-receive (T/R) switch580 in the transmit path that couples to a receiver amplifier 490.

It will be understood that if the phase-frequency detector 537 isdifficult to implement as a low current standard integrated circuitsolution then a standard active analog phase detector such as a Gilbertcell mixer can be used. Assisted acquisition techniques then may be usedto provide fast lock times for the PLL.

FIG. 9 is a block diagram of modulation systems and methods according toother embodiments of the present invention. FIG. 9 illustrates dual modemodulation systems and methods 900 that can produce cellular and PCSsignals. As shown in FIG. 9, a phase locked loop includes phasefrequency detector or phase detector 1140 and a low pass filter 1144 a,1144 b and a controlled oscillator such as a VCO 1142 a, 1142 b for eachmode. A main local oscillator 534 and a pair of mixers 533 a, 533 b alsoare provided. An amplitude tracking subsystem 440′″ also may beresponsive to a power control signal 1110. A pair of variable gainamplifiers and/or power amplifiers 1150 a, 1150 b may be provided. Alimiter 1120 also is provided between the modulator 420 and the phasefrequency detector 1140.

In summary, embodiments of FIGS. 4–9 can deliver low-distortion complexmodulation signals containing both amplitude and phase information, withvery high signal-to-noise ratio (for example on the order of −165 dBc/Hzat 45mHz offset) to a power amplifier. These embodiments can reduce oreliminate the need for SAW filters that are traditionally used inconventional digital radio transmitter architectures. They also canreduce power consumption and spurious products compared to theconventional up-mixing transmitters.

Referring now to FIG. 10, a block diagram of other embodiments ofmodulation systems and methods according to the present invention isshown. As shown in FIG. 10, these modulation systems and methods 1000include a Digital Signal Processor (DSP) 920 that generates in-phase(I), quadrature-phase (Q) and amplitude (A) signals 922, 924 and 926,respectively, from a baseband signal 912 that may be generated by a userinterface 910. A modulator such as an IQ modulator 930 modulates thein-phase and quadrature-phase signals 922 and 924, respectively, toproduce a modulated signal 932. A phase locked loop 940 is responsive tothe modulated signal. The phase locked loop 940 includes a controlledoscillator 942 having a controlled oscillator output 944. An amplifier950 includes a signal input, an amplitude or gain control input and anoutput. The signal input is responsive to the controlled oscillatoroutput 944 and the amplitude control input is responsive to theamplitude signal 926. An optional power amplifier 960 is responsive tothe output of the amplifier 950. A transmit antenna is responsive to thepower amplifier 960 and/or amplifier 950.

FIG. 11 illustrates other modulation systems and methods 1100 accordingto embodiments of the present invention. As shown in FIG. 11, thedigital signal processor 920′ generates in-phase I and quadrature-phaseQ signals 923 and 925, respectively, from a baseband signal 912 at theinput 921 thereof. A generator 928 within the digital signal processor920′ then generates normalized in-phase (I′) and quadrature-phase (Q′)signals 922′ and 924′ and a normalized amplitude signal 926′. It will beunderstood that the generator 928 may be embodied as a hardware and/orsoftware module in the digital signal processor 920′, and that thesignals 922′, 924′ and 926′ may be generated directly from the basebandsignal 912, without the need to generate the intermediate signals 923,925. The normalized in-phase and quadrature signals 922′ and 924′ areapplied to a modulator such as an IQ modulator 930, such that themodulated signal 936 is of constant amplitude, followed by a phaselocked loop 940, amplifier 950, optional power amplifier 960 and antenna970 as was described in connection with FIG. 9. The normalized amplitudesignal A′ is applied to the gain control input of the amplifier 950.

Still referring to FIG. 11, in embodiments of the invention, the digitalsignal processor 920′ generates the normalized in-phase signal I′922′ asa cosine of an angle θ and generates the normalized quadrature-phasesignal Q′924′ as a sine of the angle θ, where the angle θ is an anglewhose tangent is the quadrature-phase signal 925 divided by the in-phasesignal 923. Moreover, the normalized amplitude signal 926′ is generatedas the square root of the sum of the in-phase signal I 923 squared andthe quadrature-phase signal Q 925 squared. It will be understood thatthe sine and cosine functions may be interchanged from that which isdescribed above.

Embodiments of FIGS. 10 and 11 can mathematically manipulate I, Q and Asignals to allow reduced distortion in modulators. Conventionally, I andQ signals come from the baseband section of a wireless terminal carryingthe modulating information that represents a voice and/or data signalthat is to be transmitted. I and Q signals also can be represented asamplitude and phase signals. As was already described, a conventionaltransmitter modulates a VCO with this I and Q information and thenamplifies the composite signal and up-converts the frequency to thetransmit frequency. In sharp contrast, embodiments of FIGS. 10 and 11perform numerical generation of I, Q and A signals from baseband.Moreover, embodiments of FIG. 11 generate normalized I, Q and A signalsI′, Q′ and A′, respectively, from baseband. This can eliminate the needfor a limiter to inject the signals into the phase locked loop of anrTheta architecture. The amplitude signal A′ may be generatednumerically from baseband such that an envelope detector may not beneeded for the analog reconstruction of that signal. Amplitude directfrom baseband also can allow flexible phase shifting between amplitudeand phase waveforms for rTheta architectures.

More particularly, conventional modulating systems, for example asillustrated in FIGS. 1, 2 and 3, generate amplitude information from theIQ signal so that the rest of the transmitter chain may need to belinear enough to meet desired modulation specifications. In contrast, ifthe amplifiers can be saturated instead of linear, current consumptionmay be reduced. Moreover, conventional modulation systems may have lowlevels of linearity for a given current consumption. This may beespecially true for modulation schemes whose peak-to-average is not afundamental limit and even further back-off may be needed to satisfynear channel interference levels.

Moreover, embodiments of FIG. 9 may produce an amplitude control signal442 that may not be ideal because of distortion caused in the IQmodulator 420. The amplitude tracking circuit 440′″ also may causedistortion. It also may be generally desirable to place a limiter 1120between the IQ modulator 420 and the phase locked loop to removeunwanted amplitude information. The limiter 1120 may cause AM/PMdistortion in the phase signal 432 a, 432 b and also can cause unwanteddelay between the amplitude and phase signals when they are combined atthe driver stages 1150 a and 1150 b.

In contrast, embodiments of FIGS. 10 and 11 can calculate a desiredoutput for an amplitude tracking subsystem 440 (FIG. 4) and can applythis output directly. Moreover, a limiter may not be needed becauselimiting may already be incorporated into the generation of the I′ andQ′ signals.

FIG. 12 is a block diagram of modulating systems and methods accordingto other embodiments of the present invention. As shown in FIG. 12, aDSP 920′ generates an I′ signal 922′, a Q′ signal 924′ and an A′ signal926′ from a baseband signal 912. A controlled oscillator 910 and the I′and Q′ signals 922′ and 924′, respectively, are applied to an IQmodulator 930 to produce a modulated signal 932 that is applied to aphase frequency detector or phase detector 940 including a pair of lowpass filters 944 a, 944 b and a pair of controlled oscillators 942 a,942 b. Also applied to the phase frequency detector 940 is a main localoscillator 990 modulated by second modulators 992 a, 992 b. The outputof the controlled oscillators 942 a, 942 b are applied to amplifiers 950a and 950 b, respectively, which can be variable gain amplifiers and/orother conventional amplifiers such as power amplifiers or driveramplifiers. As also shown in FIG. 12, amplitude control also may becombined with a power control signal 982 in a combined power control andamplitude control module 980. Accordingly, an improved rThetaarchitecture may be provided. FIG. 13 is a block diagram of a singleband version of FIG. 12.

The following equations show how the I′, Q′ and A′ signals may becalculated for embodiments of FIGS. 11, 12 and 13:

$\theta = {\tan^{- 1}\left( \frac{Q}{I} \right)}$The angle should be a four-quadrant representation of the I and Q-data.I′=cos θQ′=sin θThe I′ and Q′ signals also may be interchanged. Therefore, the I′ and Q′signals can be used to modulate the IF, and can create an IF that can beidentical to an IQ modulated IF signal that has passed through an ideallimiter. Since the I′ and Q′ signals can be free of amplitudeinformation, a limiter may not be needed at the input of thephase-frequency detector of the phase locked loop. Phase distortion, orAM/PM distortion that may occur in a real limiter, also may be reducedor eliminated.

The A′ signal is calculated as follows:A′=√{square root over (I ² +Q ² )}Since the A′ signal is calculated mathematically and applied directly tothe amplifier, it need not contain any of the distortion created in theIQ modulation of the IF, and it also need not contain any distortionfrom the amplitude detector circuit.

Accordingly, limiters/envelope detectors may be removed and relatedAM/PM distortion may be reduced or eliminated. VCO pulling also may beremoved that may arise from amplitude variations on a phase only signal.Sending the amplitude directly from baseband can result in exact andrepeatable power control, as well as flexibility in phase shifting ofamplitude relative to phase only signals in rTheta transmitters.

Embodiments of the invention that were described in FIGS. 4–13 placedthe quadrature modulator prior to the phase locked loop. Thus, forexample, in FIGS. 4–8, the IQ modulator 420 modulates in-phase andquadrature phase signals, and provides a modulated signal 422 to a phaselocked loop in a phase tracking system 430 or 430′. Similarly, in FIGS.10–11, the IQ modulator 930 modulates I and Q signals and provides themodulated signal 932 to a phase locked loop 940. Thus, in theseembodiments, the IQ modulation may take place at the IF frequency bydirectly modulating the IF reference signal.

According to other embodiments that will be described below inconnection with FIGS. 14–22, modulation is applied within the phaselocked loop itself. In particular, the phase locked loop includes acontrolled oscillator having a controlled oscillator input and acontrolled oscillator output, and a feedback loop between the controlledoscillator input and the controlled oscillator output. The feedback loopincludes a mixer that is responsive to a local oscillator. In someembodiments, the modulator is placed in the feedback loop between thecontrolled oscillator output and the mixer, between the local oscillatorand the mixer, or between the mixer and the controlled oscillator input.Accordingly, the modulation can be applied by modulating a localoscillator signal and leaving the IF as an unmodulated signal.Alternatively, the modulation can be applied to the RF output, and thenmixed with an unmodulated local oscillator and IF frequency. In yetanother alternative, the modulation may be performed after the mixer inthe feedback path of the phase locked loop if it is desired to keep theIQ modulator running at the IF frequency.

For example, FIG. 14 is similar to FIG. 4, except that the IQ modulator420 is included within the phase tracking subsystem 430″, preferablywithin the feedback loop of the phase locked loop of the phase trackingsubsystem 430″. FIG. 15 is similar to FIG. 10, except the IQ modulator930 is included within the phase locked loop 940′, preferably within thefeedback loop thereof.

FIG. 16 is a block diagram of embodiments of the invention thatillustrate various alternative locations of the IQ modulator within thephase locked loop. It will be understood that FIG. 16 can correspond tothe phase tracking system 430 of FIG. 4, 430′ of FIGS. 5–8 and/or 430″of FIG. 14, and/or the phase locked loop 940 of FIGS. 10–13, and/or 940′of FIG. 15.

As shown in FIG. 16, the phase locked loop 1600 includes a phasedetector or phase-frequency detector 1620 that can correspond to thephase-frequency detector or phase detector 537 of FIGS. 5–8, 1140 ofFIG. 9 and/or 940 of FIGS. 12–13, and a low pass filter 1630 that cancorrespond to the low pass filter 538f FIGS. 5–8, 1144 a of FIG. 9,and/or 944 a of FIG. 12. A controlled oscillator, such as a VoltageControlled Oscillator (VCO) 1640 can correspond to the VCO 532 of FIGS.5–8, 1142 a, 1142 b of FIG. 9, 942 a, 942 b of FIG. 12 and/or 942 ofFIGS. 10, 11, 13 and 15. As also shown in FIG. 16, the controlledoscillator has a controlled oscillator input 1604 and a controlledoscillator output 1606. A feedback loop 1602 is provided between thecontrolled oscillator output 1606 and the controlled oscillator input1604 via the phase-frequency detector or phase detector 1620 and lowpass filter 1630. The feedback loop includes a mixer 1660 that cancorrespond to the mixer 533 of FIGS. 5–8, 533 a, 533 b of FIG. 9, 922 a,922 b of FIG. 12 and/or 922 of FIG. 13, and a local oscillator 1680 thatcan correspond to the local oscillator 534 of FIGS. 5–9 and/or 990 ofFIGS. 12–13.

In FIG. 16, four possible locations of the IQ modulator corresponding toIQ modulator 420 of FIGS. 4–9 and/or 930 of FIGS. 10–13 are shown by IQmodulators 1610, 1650, 1670 and 1690. It will be understood by thosehaving skill in the art that only one IQ modulator need be provided atonly one of the positions shown in FIG. 16. However, multiple IQmodulators also may be provided.

The IQ modulator 1610 is placed prior to the phase locked loop 1600 in amanner corresponding to FIGS. 4–13 as was described extensively above.The IQ modulator 1650 is placed in the feedback loop 1602 between thecontrolled oscillator output 1606 and the mixer 1660. The IQ modulator1670 is placed in the feedback loop 1602 between the local oscillator1680 and the mixer 1660. Finally, the IQ modulator 1690 is placed in thefeedback loop 1602 between the mixer 1660 and the controlled oscillatorinput 1604.

When the IQ modulator 1650 is placed between the output of thecontrolled oscillator 1606 and the mixer 1660, the RF output signal ofthe controlled oscillator 1640 is modulated with the I and Q signals.Thus, this is an example of RF modulation. When the IQ modulator 1690 isplaced between the mixer 1660 and the controlled oscillator input 1604,this can correspond to IQ modulating at the IF frequency, but themodulation takes place in the feedback loop 1602 of the phase lockedloop 1600, rather than at the IF input, as would be the case withmodulator 1610. When the modulator 1670 is placed between the localoscillator 1680 and the mixer 1660, the local oscillator frequency ismodulated before it is mixed with the RF to create the IF feedbacksignal. The phase can be preserved through the mixer, so that ananalogous situation to modulating with modulator 1610 may be provided.

It will be understood by those having skill in the art that each of thefour positions of the modulators 1610, 1650, 1670 and 1690 shown in FIG.16 can provide the same result at the output. Various considerations maybe used in deciding where to place the modulator. For example, it may bemore efficient to IQ modulate at the IF frequency, so that modulators1610 and 1690 may be preferred. Modulating at RF (modulator 1650) or atthe local oscillator (modulator 1670) may consume more current thanmodulating at IF. However, the current consumption may depend on thefrequency plan of the system. It also will be understood that anamplitude signal may be generated and/or applied in a manner that wasdescribed in any of the previous figures.

FIG. 17 is a block diagram that is similar to FIG. 5, except the IQmodulator 1650 is placed in the feedback loop between the output of thecontrolled oscillator 532 and the mixer 533, rather than the IQmodulator 420 of FIG. 5. An IQ modulator 1670 or 1690 of FIG. 16 alsomay be used in embodiments of FIG. 17.

FIG. 18 illustrates the use of an IQ modulator 1670 between the localoscillator 534 and the mixer 533, instead of the IQ modulator 420 at theinput of the phase locked loop in FIG. 6. It will also be understoodthat an IQ modulator 1650 or 1690 of FIG. 16 also may be employed.

FIG. 19 illustrates the use of an IQ modulator 1690 between the mixer533 and the input of the controlled oscillator 532, instead of the IQmodulator 420 of FIG. 7. It also will be understood that IQ modulators1650 or 1670 also may be used. IQ modulators also may be used in thepositions shown in FIG. 16 in other embodiments of the inventionaccording to FIGS. 8 and 9.

FIG. 20 illustrates the use of a modulator 1650 between the output ofthe controlled oscillator 942 and the mixer 992, instead of the IQmodulator 930 of FIG. 13. FIG. 21 illustrates an IQ modulator 1670between the local oscillator 990 and the mixer 992, instead of the IQmodulator 930 of FIG. 13. FIG. 22 illustrates an IQ modulator 1690between the mixer 992 and the input of the controlled oscillator 942,instead of the IQ modulator 930 of FIG. 13. Similar placements of themodulator may be provided for the embodiments of FIG. 12.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

1. A modulation system comprising: a quadrature modulator that modulatesin-phase and quadrature-phase signals to produce a modulated signal; aphase tracking subsystem that is responsive to the quadrature modulatorto produce a phase signal that is responsive to phase changes in themodulated signal and that is independent of amplitude changes in themodulated signal; an amplitude tracking subsystem that is responsive tothe quadrature modulator to produce an amplitude signal that isresponsive to amplitude changes in the modulated signal and that isindependent of phase changes in the modulated signal; and an amplifierhaving a signal input, an amplitude control input and an output, whereinthe signal input is responsive to the phase signal and the amplitudecontrol input is responsive to the amplitude signal; wherein the phasetracking subsystem comprises a phase locked loop that includes acontrolled oscillator having a controlled oscillator input, a controlledoscillator output that produces the phase signal and a feedback loopbetween the controlled oscillator input and the controlled oscillatoroutput, the feedback loop including a mixer that is responsive to alocal oscillator, and wherein the quadrature modulator is includedwithin the feedback loop between the controlled oscillator output andthe mixer, between the local oscillator and the mixer, or between themixer and the controlled oscillator input.
 2. A system according toclaim 1 wherein the amplitude tracking subsystem comprises an automaticgain control subsystem that is responsive to the modulated signal toproduce the amplitude signal.
 3. A system according to claim 1 whereinthe phase tracking system further comprises a limiter between thequadrature modulator and the phase locked loop.
 4. A system according toclaim 1 further comprising: a power amplifier that is responsive to theoutput of the amplifier having a signal input, an amplitude controlinput and an output; and a transmit antenna that is responsive to thepower amplifier.
 5. A system according to claim 1 further comprising atransmit antenna that is responsive to the output of the amplifier and auser interface that generates the in-phase and quadrature signals inresponse to user input, to provide a wireless communications terminal.6. A system according to claim 1 wherein the amplifier is a poweramplifier.
 7. A modulation system comprising: a quadrature modulatorthat modulates in-phase and quadrature-phase signals to produce amodulated signal; a phase tracking subsystem that is responsive to thequadrature modulator to produce a phase signal that is responsive tophase changes in the modulated signal and that is independent ofamplitude changes in the modulated signal; an amplitude trackingsubsystem that is responsive to the quadrature modulator to produce anamplitude signal that is responsive to amplitude changes in themodulated signal and that is independent of phase changes in themodulated signal, wherein the amplitude tracking subsystem comprises anautomatic gain control subsystem that is responsive to the modulatedsignal to produce the amplitude signal; an amplifier having a signalinput, an amplitude control input and an output, wherein the signalinput is responsive to the phase signal and the amplitude control inputis responsive to the amplitude signal; wherein the phase trackingsubsystem comprises a phase locked loop that includes a controlledoscillator having a controlled oscillator output that produces the phasesignal and wherein the quadrature modulator is included within the phaselocked loop; and wherein the automatic gain control subsystem furthercomprises: a first envelope detector that is responsive to the modulatedsignal; a second envelope detector that is responsive to the phaselocked loop; and a comparator that is responsive to the first and secondenvelope detectors to produce the amplitude signal.
 8. A modulationsystem comprising: a quadrature modulator that modulates in-phase andquadrature-phase signals to produce a modulated signal; a phase trackingsubsystem that is responsive to the quadrature modulator to produce aphase signal that is responsive to phase changes in the modulated signaland that is independent of amplitude changes in the modulated signal; anamplitude tracking subsystem that is responsive to the quadraturemodulator to produce an amplitude signal that is responsive to amplitudechanges in the modulated signal and that is independent of phase changesin the modulated signal, wherein the amplitude tracking subsystemcomprises an automatic gain control subsystem that is responsive to themodulated signal to produce the amplitude signal; an amplifier having asignal input, an amplitude control input and an output, wherein thesignal input is responsive to the phase signal and the amplitude controlinput is responsive to the amplitude signal; wherein the phase trackingsubsystem comprises a phase locked loop that includes a controlledoscillator having a controlled oscillator output that produces the phasesignal and wherein the quadrature modulator is included within the phaselocked loop wherein the automatic gain control subsystem furthercomprises: a first envelope detector that is responsive to the modulatedsignal; a second envelope detector that is responsive to the amplifier;and a comparator that is responsive to the first and second envelopedetectors to produce the amplitude signal.
 9. A modulation systemcomprising: a quadrature modulator that modulates in-phase andquadrature-phase signals to produce a modulated signal; a phase trackingsubsystem that is responsive to the quadrature modulator to produce aphase signal that is responsive to phase changes in the modulated signaland that is independent of amplitude changes in the modulated signal; anamplitude tracking subsystem that is responsive to the quadraturemodulator to produce an amplitude signal that is responsive to amplitudechanges in the modulated signal and that is independent of phase changesin the modulated signal; an amplifier having a signal input, anamplitude control input and an output, wherein the signal input isresponsive to the phase signal and the amplitude control input isresponsive to the amplitude signal; wherein the phase tracking subsystemcomprises a phase locked loop that includes a controlled oscillatorhaving a controlled oscillator output that produces the phase signal andwherein the quadrature modulator is included within the phase lockedloop; and wherein the amplitude tracking subsystem further comprises anenvelope detector that is responsive to the modulated signal to producethe amplitude signal.
 10. A modulation method comprising: modulatingin-phase and quadrature signals to produce a modulated signal; producinga phase signal from the modulated signal that is responsive to phasechanges in the modulated signal and that is independent of amplitudechanges in the modulated signal using a phase locked loop that includesa controlled oscillator having a controlled oscillator input, acontrolled oscillator output and a feedback loop between the controlledoscillator input and the controlled oscillator output, the feedback loopincluding a mixer that is responsive to a local oscillator, wherein themodulating is performed in the feedback loop between the controlledoscillator output and the mixer, between the local oscillator and themixer, or between the mixer and the controlled oscillator input;producing an amplitude signal from the modulated signal that isresponsive to amplitude changes in the modulated signal and that isindependent of phase changes in the modulated signal; and amplifying thephase signal at a gain that is varied in response to the amplitudesignal.
 11. A method according to claim 10 wherein the producing anamplitude signal from the modulated signal comprises automatic gaincontrolling the modulated signal to produce the amplitude signal.
 12. Amethod according to claim 10 further comprising limiting the modulatedsignal, and wherein the applying the modulated signal to a phase lockedloop comprises applying the limited modulated signal to a phase lockedloop that includes a controlled oscillator having a controlledoscillator output that produces the phase signal.
 13. A method accordingto claim 10 further comprising: transmitting the amplified phase signal.14. A method according to claim 13 further comprising: generating thein-phase and quadrature signals in response to user input, to provide awireless communications method.
 15. A modulation method comprising:modulating in-phase and quadrature signals to produce a modulatedsignal; producing a phase signal from the modulated signal that isresponsive to phase changes in the modulated signal and that isindependent of amplitude changes in the modulated signal using a phaselocked loop that includes a controlled oscillator having a controlledoscillator output, wherein the modulating is performed within the phaselocked loop; producing an amplitude signal from the modulated signalthat is responsive to amplitude changes in the modulated signal and thatis independent of phase changes in the modulated signal; amplifying thephase signal at a gain that is varied in response to the amplitudesignal; wherein the producing an amplitude signal from the modulatedsignal comprises automatic gain controlling the modulated signal toproduce the amplitude signal; and wherein the automatic gain controllingcomprises: envelope detecting the modulated signal; envelope detecting asignal in the phase locked loop; and comparing the envelope detectedmodulated signal and the envelope detected signal in the phase lockedloop to produce the amplitude signal.
 16. A modulation methodcomprising: modulating in-phase and quadrature signals to produce amodulated signal; producing a phase signal from the modulated signalthat is responsive to phase changes in the modulated signal and that isindependent of amplitude changes in the modulated signal using a phaselocked loop that includes a controlled oscillator having a controlledoscillator output, wherein the modulating is performed within the phaselocked loop; producing an amplitude signal from the modulated signalthat is responsive to amplitude changes in the modulated signal and thatis independent of phase changes in the modulated signal; amplifying thephase signal at a gain that is varied in response to the amplitudesignal; wherein the producing an amplitude signal from the modulatedsignal comprises automatic gain controlling the modulated signal toproduce the amplitude signal; and wherein the automatic gain controllingcomprises: envelope detecting the modulated signal; envelope detectingthe amplified phase signal; and comparing the envelope detectedmodulated signal and the envelope detected amplified phase signal toproduce the amplitude signal.
 17. A modulation method comprising:modulating in-phase and quadrature signals to produce a modulatedsignal; producing a phase signal from the modulated signal that isresponsive to phase changes in the modulated signal and that isindependent of amplitude changes in the modulated signal using a phaselocked loop that includes a controlled oscillator having a controlledoscillator output, wherein the modulating is performed within the phaselocked loop; producing an amplitude signal from the modulated signalthat is responsive to amplitude changes in the modulated signal and thatis independent of phase changes in the modulated signal; amplifying thephase signal at a gain that is varied in response to the amplitudesignal; and wherein the producing an amplitude signal from the modulatedsignal comprises: envelope detecting the modulated signal to produce theamplitude signal.